Removal of inorganic sulfates from alkali metal benzenesulfonate and its homologues



Oct. 23, 1951 D. R. JACKSON l' AL REMOVAL OF INORGANIC SULFATES FROM ALKALI METAL. BENZENESULFONATE AND ITS HOMOLOGUES Filed March 23,- 1949 BY 2mm@ Attorhey Y UNITED STATES PATENT OFFICE REMOVAL OF INORGANIC SULFATES FROM ALKALI METAL BENZENESULFON ATE AND ITS HOMOLOGUES Donald R. Jackson, Wyandotte, and William K.

Langdon and Thomas H. Vaughn, Grosse Ile, Mich., assignors to Wyandotte Chemicals Corporation, Wyandotte, Mich., a corporation of Michigan Application March 23, 1949, Serial No. 82,992

7 Claims. (Cl. 26o-505) The purication of the sulfonation products of benzene and of homologues of the benzene series (e. g., toluene, xylene, cymene, etc.) has heretofore presented a dimcult problem because solved alkali metal benzenesulfonate (and aliphatically substituted homologues thereof) becomes greater than the amount of water present. Since the water solubility of the homologous alof the high content of inorganic sulfate residual kali metal benzenesulfonates increases as the in the reaction mass after neutralization of the temperature, it is a corollary to these discoveries sulfonic acid and the excess sulfuric acid. Variand our purification process founded upon them, ous attempts have been made t0 solve this probthat a suiiicient temperature must be maintained lem, over a course of many years. Brieiiy sumin the mixture from which the alkali metal sulmarized, these vprevious attempts can be outlined fate is Separated, to retain Such DTODOITOH 0f 01- as follows: (1) neutralization with lime, to pregarlic sulfonaterl Solution.

cipitate calcium sulfate, followed by metathesis Examples of the homologous alkali metal with an alkali metal hydroxide or carbonate to benzenesulfonates which can be puried accordtransform the calcium aryl sulfonate to an alkali ing to the process of our invention are as follows: metal aryl sulfonate (U. S. Patent No. 1,207,798) l5 sodium benzenesulfonate, sodium toluenesulfo- (2) treatment of the sulfonation mass with NaCl nate, sodium xylenesulfonate, sodium cymeneto precipitate out sodium benzenesulfonate, leavsulfonate, (sodium methyl benzenesulfonate) ing the inorganic sulfate in solution and recover- (sodium dimethylbenzenesulfonate) (sodium ing the puried sodium benzenesulfonate as the methyl isopropyl benzenesulfonate), and the corltration residue (U. S. Patent No. 1,396,320); 20 responding potassium, lithium and ammonium and (3) maintaining the sulfuric acid content of compounds.

the sulfonation mass at a minimum by reduction In the aliphatically substituted homologues, it of the amount of sulfonating agent (U. S. Patent will be noted that there are a total of l-4 carbon N 0. 1,547,186) atoms in such substituent groups.

Even in the prior art processes (1) and (3) 25 Our invention utilizes and makes practical apabove, the amount of inorganic sulfate contamiplication of the above mentioned discoveries in nant remaining in the aryl sulfonate product, is the form of the following described procedures: disclosed as being 0n the order of 5-15% by A. A solid mixture of the a1ka1i metal benzeneweight. (All percentages herein given are by sulfonate, or its aliphatically substituted homo- Weight.) logues, and a contaminating amount of alkali On the basis of the principle of the abovemetal sulfate present is treated with an amount mentioned U- S- Patent N0. 1,396,320. it WOuld of water sufficient to dissolve the amount of ornormally be expected that an inorganic salt such ganic sulfonate alone which is present. The as Na2SO4, in an aqueous medium, would salt out organic sulfonate thereby takes up the water in the organic sulfonate. Directly contrary to such preference to the inorganic sulfate. The undisexpectation, however, we have discovered that solved sulfate is then easily removed by filtering the organic sulfonate :salts out the inorganic sulor centrifuging. Preferably such treatment is fate, i. e. the organic sulfonate dissolves in the conducted at above room or atmospheric temwater in preference to the inorganic sulfate. perature, viz: from 30 C. to the solution boiling In its broader aspect, therefore, our invention point. Such increased temperature treatment in comprises the removal of alkali metal sulfates turn increases the water solubility of the organic from alkali metal benzenesulfo'nates and the sulfonate to the further inhibition or detriment aliphaticallv substituted homologues thereof, by of the solubility of the inorganic Sonate. preparing a water Asuspension of the sulfonate- This procedure A is further illustrated by the sulfate mixture wherein the sulfonate becomes following tabulated results which were obtained completely dissolved and a large proportion or by treating a solid, dry mixture of approximately substantially al1 of the sulfate remains undis- 2 parts sodium xylenesulfonate and l part sodium solved; the organic sulfonate with its Na2SO4 sulfate (i. e. of about 33% NazSOi content) with content reduced then being obtainable in solid an amount of water sufficient to dissolve all of form by evaporation or drying. the sulfonate alone. (A saturated solution of We have also discovered that in the threesodium xylenesulfonate solution at room temcomponent system consisting of homologous perature is of about 40% concentration.) Such benzenesulfonates, water and inorganic alkali water treatment was conducted at temperatures metal Asulfate the latter approaches practically of Y30 C. and above, thereby preferentially discomplete insolubility when the proportion of dis'- 55 solving out the sulfonate, and ltering:

Per Cent SulfonateXlOO Tempera. isglligse N325()4 in Sulionate H ture, C C. Filtrate 2 Filtrate Solids 39. 6 30 46. 6 25. 8 39. 6 40 46. 2 23. 5 39. 9 60 45. 8 21. 4 4U. 4 60 45. 9 20. 1 40. 4 75 45. 4 18. 4 40. l 85 44. 8 17. 6 40. 3 95 44. 9 17. 2 43. 6 34 47. 9 15. 7 46. 4 50 49. 0 13. 5 46. 7 75 481. 7 12. 4 46. 4 97 4T. 7 13. 4 52. 2 48 54. 5 8.9 62. 4 64 63. 0 2. 5

From these results it will be seen that as the factors promoting the water dissolution of greater proportions of sodium xylene sulfonate are increased, the amount of NazSOi going into solution decreases with a corresponding increase in Ythe amount separated from the original sulfonate-sulfate mixture.

B. The alkali metal benzenesulfonate or an aliphatically substituted homologue thereof, containing a contaminating amount of inorganic sulfate, (on the order of -75%, total solids basis) is mixed with water in such proportion that the benzenesulfonate is greater than the amount of water present. The temperature of such mixture is maintained between the minimum required for dissolving the amount of the benzenesulfonate and the boiling point of the solution. Due to the decreased solubility of the inorganic sulfate in such a solution, excess amounts thereof, remain undissolved and are separated by a suitable removal process such as by way of filtration or centrifuging. Preferably this purification process is conducted at a concentration of 60 parts and greater of the organic sulfonate per 100 parts of sulfonate and water because the solubility of the inorganic sulfate in the sulfonate solution is sharply and distinctly decreased at such a critical concentration limit. The corresponding preferred temperature range :for such organic sulfonate concentrations is 60-115" C.

C. Our purification process is also Performed by evaporating an organic sulfonate-inorganic sulfate-water mixture to increase the sulfonate content to above the water content, and separating the undissolved inorganic sulfate at a temperature sufficiently high to maintain the organic sulfonate in solution.

D. The process of our invention is also performed as a part of the over-al1 process for synthesizing alkali metal benzenesulfonate and its homologues. This particular form of practice of our process is of Special advantage in that it permits the use of a substantial excess of sulfonating agent, such as sulfuric acid or oleum, thus contributing to a high yield and rapidity of the sulfonation reaction. The sulfonation reaction mass, containing the sulfonic and sulfuric acids, is then neutralized with a neutralizing agent such as caustic soda. The amount of water present in the neutralized sulfonation mass is controlled by the amount present in the neutralizing agent solution, by the amount which may be added by way of drowning the sulfonation mass, or by the amount which may be removed by evaporation or distillation. This amount of water is adjusted to within a maximum corresponding to less than the amount of organic sulfonate present. Preferably, the neutralization is conducted at temperatures of (S0-115 C., whereby the heat of neutralization may be utilized and the operation conducted in the temperature range wherein the organic sulfonate is maintained in solution. The neutralized reaction mass is then ltered at the elevated temperature range whereby the precipitated and undissolved inorganic sulfate is removed.

As a result of our above described process, it is possible to remove the contaminating inorganic sulfate to an amount of less than 1% by weight on the total solids content basis. In any event, our process makes it possible to purify alkali metal benzenesulfonate and homologues thereof, by the removal of inorganic sulfate, to an extent greater than that heretofore achieved in the art (by other than liming treatment), and by the elimination of the more costly, more complicated and greater time-consuming treatments and processes heretofore known.

The following specific examples illustrate in detail the manner in which the foregoing procedures may be carried out:

EXAMPLE 1 Sodium benzenesulfonate A mixture containing 900 grams of sodium benzenesulfonate, 538 grams of sodium sulfate and 1148 grams of water (weight ratio of sodium benzenesulfonate to water=44z56l was stirred and heated at 95 C. in order to obtain solubility equilibrium. Aiter the mixture had been filtered at 95 C. and analysis of the filtrate indicated that the total solids contained 6.7% of sodium sulfate. The filtrate was further concentrated until the weight ratio of sodium benzenesulfonate to water was :50 and it was again ltered at 95 C. An analysis of the filtrate showed that the total solids contained 3.8% of sodium sulfate. Thus, the Na2SO4 content of the original mixture was reduced from 37% to 3.8%, total solids basis.

EXAMPLE 2 Sodium toluenesulfonate Toluene was sulfonated with an excess of 98% sulfuric acid at a final temperature of 100 C. When the reaction was completed the sulfonation mass was neutralized with 50% caustic soda and filtered at 90 C. The calculated ratio of sodium toluenesulfonate to water in this mixture was 58 t 42. An analysis of the filtrate showed that the total solids contained 2.2% of sodium sulfate.

EXAMPLE 3 Sodium toluenesulfvnate Five moles of toluene was sulfonated with 7.6 moles of 98% sulfuric acid. The sulfonation mass was heated at 100 C. for two hours after the acid had been added to the toluene. After drowning the sulfonation mass in Water it was neutralized with 50% caustic soda and ltered at 90 C. The calculated ratio of sodium toluenesulfonate to water in this mixture was 45 55 and it is estimated that about three fourths of the sodium sulfate present was removed in this ltration. The filtrate was then concentrated by evaporation of water until it contained parts of sodium toluenesulfonate per 40 parts of Water. This concentrate was then ltered at C. and analysis of the ltrate showed that the total Solids contained 2.25% of sodium sul- EXAMPLE 4 S odium ylenesuljonate vXylene or :dimethylbenzena 'of a commercially pure grade (consisting essentially of metaxylene and containing lesser amounts of .the orthoand para isomers) in the amount of 318 grams, or 3 mols, was placed in a l-lte-r 3-necked ask equipped with an addition funnel, mechanical stirrer, reux condenser and thermometer.. The flask was heated with an electric heating mantle. Sulfuric acid `(98% concentration) in Athe-amount of 456 grams (4.5 mols or a 50% excess of the chemically .equivalent amount vrequired to react with the xylene) was. .added over .an `S-minute period during which the temperature rosev from ,20 to 100 C. After the addition of the sulfuric acid, 'the 4temperature Was maintained 'in the range of 98-105 C. for one hour. The resultant sulfonation mass was then transferred to a separatory funnel and allowed to stand over night. One portion of the sul-fonation mass was neutralized with V50% caustic `soda at a temperature 'of 90-11-5" C. The precipitated NazSQi was then removed by filtration at about 80 C. The Yanalysis of the-filtrate was found to be 59.7% of solids and 0.52% NazSOi, equivalent to 0.86% total solids basis. A second portion of this sulfonation mass was similarly neutralized and filtered, but at a lower temperature of approximately 60 C. The analysis of this latter ltrate was found to be 60.3% total solids of which there was 1.77% Na2SO4.

EXAMPLE 5 Sodium .ylenesulfouate Xylenev in the amount of 530 pounds and 98% sulfuric acid in the amount of 760 pounds were charged into a sulfonator and reacted for one hour fat 100 C.Y The entire :sulfonation mass, after cool-ing, was drowned in 11000 pounds-ofwater and neutralized to a pH of about 8.0 with 50% caustic soda solution. The material was then filtered under reduced pressure through canvas using a lter aid, at a) temperature of 85-90 C. After filtration, the ltrate was concentrated by distillation to a content corresponding to approximately 60% of sodium xylenesulfonate. The precipitated sodium sulfate was then separated by filtration through a filter press Iat a temperature of 95 C. The filtrate was adjusted with water to make an approximately 40% sodium xylenesulfonate solution which, on analysis was found to contain only 0.60% NazSOi, equivalent to 1.4% total solids basis.

EXAMPLE 6 Sodium p-cymenesulfonate Five moles of p-cymene was sulfonated with 5% oleum containing the equivalent of 10 moles of S03. After drowning the sulfonation mass in water and neutralizing with 50% caustic soda, it was calculated that the ratio of sodium cymenesulfonate to Water was 45 55. When this mixture was ltered at 95 C. an analysis of the filtrate showed that the total solids in the ltrate contained 12.6% of sodium sulfate. The filtrate was further concentrated to a sulfonate-water ratio of 610 40 and again ltered at 95 C. Analysis of the filtrate showed that the total solids contained 3.5 of sodium sulfate.

In the foregoing examples the original organic sulfonate product was contaminated with Na2SO4 on the order of 331/3 total solids basis. By our 6 process the' 'NasSGi wasfreduced to less .than 1%, and at the most not over 4%.

The 'figure in the -annexed drawing is a .chart which further illustrates this unusual solubility property of sodium sulfate in homologous :benzenesulfonate .aqueous solutions, and the principle upon which our invention is based. In the .case of the curves shown 1in this chart, the specific Iaromatic sulfonate employed is sodium xylenesulfonate. :Corresponding values and curves `for the other benzenesulfonate homologues so closely parallel those given in the chart that it is `not believed necessary .to here duplicate them.

The .curve l in the chart, represents the solubility (in zterms of parts of organic sulfonate per parts of organic .sulfonate and water) of ya saturated .aqueous solution of pure sodium xylenesulfonate with varying temperatures.

vThe lcurve 2` represents the solubility of NazSOi (total .solids .content basis) in saturated sodium xylenesulfonate solutions. It will be seen that as the amount of sodium xylenesul'fonate in solution `:becomes-greater than 50 or greater than the amount of water present, the solubility of NazSO4 therein becomes less than 5%. At the point A corresponding to a 60% sodium xylenesulfonate content solution (at 60 0.), the curve 2 reaches a value of less than 2% Na2SO4 content. The remainder of the curve'to `the right of the point A and marked 2', represents the NazSOi content of 60% sodium xylenesulfonate solutions (less than saturated) at temperatures above 60 C. The dotted straight line 3 denotes suchA 60% sodium xylenesulfonate solutions. Our process is operable at sodium xylenesulfonate concentrations above those represented by the line 3 to produce even 'higher degrees of NazSOi separation (i. e. lower Na2SO4 content of solutions) than represented by the curve 2. Thus the shaded zone of the chart demarks the practical operating ranges of organic sulfonate concentration and -of temperature for purifying such compounds contaminated with alkali metalsulfates, to the extent of less than 2% sulfate content.

Other modes of applying the principle of our invention may be employed, changes being made as regards to the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

We, therefore, particularly point out and distinctly claim as our invention:

l. The method of removing alkali metal sulfate from a compound selected from the group consisting of an alkali metal benezenesulfonate and aliphatically substituted homologues thereof wherein the said aliphatic groups comprise a total of 1-4 carbon atoms, which comprises forming an aqueous mixture of these salts with sufficient water to dissolve all of the sulfonate, the amount of sulfonate in said mixture being greater than the amount by weight of water, maintaining the temperature of this mixture between that which is required to dissolve all of the sulfonate and the boiling point of the solution, and separating the resultant solution from the undissolved inorganic sulfate.

2. The method of removing sodium sulfate from a compound selected from the group consisting of a sodium benezenesulfonate and aliphatically substituted homologues thereof wherein the said aliphatic groups comprise a total of 1-4 carbon atoms, which comprises forming an aqueous mixture of these salts with sufficient water to dissolve all of the sulfonate, the amount of sulfonate in said mixture being greater than the amount by weight of water, maintaining the temperature of this mixture between that which is required to dissolve all of the sulfonate and the boiling point of the solution, and separating the resultant solution from the undissolved inorganic sulfate.

3. The method of removing sodium sulfate from :sodium xylenesulfonate, which comprises forming an aqueous mixture of these salts with suiicient water to dissolve all of the sulfonate, the amount of sulfonate in said mixture being greater than the amount by weight of water, maintaining the temperature of this mixture between that which is required to dissolve all of the sulfonate and the boiling point of the solution, and separating the resultant solution from the undissolved inorganic sulfate.

4. The method of removing sodium sulfate from sodium toluenesulfonate, which comprises forming an aqueous mixture of these salts with suiicient water to dissolve all of the sulfonate, the amount of sulfonate in said mixture being greater than the amount by weight of water, maintaining the temperature of this mixture between that which is required to dissolve all of the sulfonate and the boiling point of the solution, and separating the resultant solution from the undissolved inorganic sulfate.

5. The method of removing sodium sulfate from sodium benzenesulfonate, which comprises forming an aqueous mixture oi these salts with suflicient water to dissolve all of the sulfonate, the amount of sulfonate in said mixture 4being greater than the amount by weight of water, maintaining the temperature of this mixture between that which is required to dissolve all of the sulfonate and the boiling point of the soution, and separating the resultant solution from the undissolved inorganic sulfate.

6. The method of removing sodium sulfate from a compound selected from the group consisting of sodium .benzenesulfonate and aliphatically 8. substituted homologues thereof wherein said aliphatic groups comprise from 1-4 carbon atoms, which comprises forming an aqueous mixture of these salts with Suiiicient water to dissolve all of the sulfonate, the amount of water being such that the ratio of sulfonate X 100 sulfonate -l-HZO is at least maintaining the temperature of this mixture between 60-95 C., and separating the resultant solution from the undissolved inorganic sulfate.

7` The method of removing sodium sulfate from sodium xylenesulfonate, which comprises forming an aqueous mixture of these salts with sufficient water to dissolve all of the sulionate, the amount of water being such that the ratio of sulfonate X sulfonate -1- H 20 is at least 60%, maintaining the temperature of this mixture between 60-95 C., and separating the resultant solution from the undissolved inorganic sulfate.

DONALD R. JACKSON. WILLIAM K. LANGDON. THOMAS H. VAUGHN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,007,327 Carr July 9, 1935 2,448,184 Lemmon Aug. 31, 1948 FOREIGN PATENTS Number Country Date 24,826 Great Britain June 13, 1907 116,934 Great Britain July 2, 1918 

1. THE METHOD OF REMOVING ALKALI METAL SULFATE FROM A COMPOUND SELECTED FROM THE GROUP CONSISTING OF AN ALKALI METAL BENEZENESULFONATE AND ALIPHATICALLY SUBSTITUTED HOMOLOGUES THEREOF WHEREIN THE SAID ALIPHATIC GROUP COMPRISE A TOTAL OF 1-4 CARBON ATOMS, WHICH COMPRISES FORMING AN AQUEOUS MIXTURE OF THESE SALTS WITH SUFFICIENT WATER TO DISSOLVE ALL OF THE SULFONATE, THE AMOUNT OF SULFONATE IN SAID MIXTURE BEING WATER THAN THE AMOUNT BY WEIGHT OF WATER, MAINTAINING THE TEMPERATURE OF THIS MIXTURE BETWEEN THAT WHICH IS REQUIRED TO DISSOLVE ALL OF THE SULFONATE AND THE BOILING POINT OF THE SOLUTION, AND SEPARATING THE RESULTANT SOLUTION FROM THE UNDISSOLVED INORGANIC SULFATE. 